The subject system and method are generally directed to the combined generation of In-phase (I) and Quadrature (Q) reference signals for a periodic input signal, and of selectively phase interpolated signals based on the same. More specifically, the subject system and method are directed to the injection locked generation of such signals in phase adjustable manner.
Sinusoidal and other such periodic signals find wide use for clocking and other purposes in a vast range of applications. A sinusoidal signal of certain frequency may be represented in a number of ways. For instance, it may be represented in polar form, with its value at any instant being defined as a phase vector, or phasor, having certain amplitude and phase offset angle values. A rotation of the phase vector one (360°) revolution about a point of origin then delineates the full range of instantaneous values described during one cycle of the sinusoid signal.
When the periodic signal's polar representation is translated onto a two-dimensional Cartesian coordinate system, the same phasor may be defined in terms of horizontal X and vertical Y coordinates with respect to a center point of origin. If the horizontal X-axis is defined as the In-phase reference (I reference) and the vertical Y axis is redefined as the Quadrature (Q) reference, each phasor may then be represented as the vector sum of respective values projected onto the I and Q references. That is, a given phasor may be uniquely represented in Cartesian coordinate form by its I and Q component values.
Thus, any phase interpolated version of a given periodic signal (or the instantaneous values of its phase vector at any phase angle position about the origin in the polar representation) may be represented in terms of the signal's I and Q references. By definition, the I and Q reference signals are versions of the same periodic signal, but with the Q reference signal lagging the I reference signal in phase by 90° (or by a quarter cycle).
Such representation of periodic signals in terms of their I and Q references is helpful in a wide range of wireless communication and other systems, particularly where data signals are modulated for reliable transmission and processing. In typical applications, a dedicated I/Q generator is utilized to formulate the I and Q references for a given periodic signal.
A separate phase interpolator circuit then formulates different phase offset versions of the periodic signal for further use. In digital applications, such as within serializer/deserializer (SerDes) systems, a periodic signal in the form of a digital clock (a train of substantially square pulses) is fed into an I/Q generator circuit which produces I Q, Ī, and Q reference signals (which represent the clock at 0°, 90°, 180°, and 270° phase offsets). These signals then serve as reference inputs to the phase interpolator circuit, by which a clock of any arbitrary phase offset may be produced.
Unfortunately, generating I and Q references (and its Ī and Q counterparts) using systems and techniques heretofore known is not a trivial matter. One widely used technique takes a clock signal of twice the desired frequency and generates I and Q references by dividing (by a factor of 2) at the rising and falling edges of each clock pulse. If the original clock signal were of 50% duty cycle, the resulting waveforms would define a frequency half that of the original clock frequency and exhibit a mutual offset in phase of one quarter cycle, or 90°. The leading waveform would define the I reference, while the other waveform would define the Q reference.
An obvious disadvantage of this approach to I/Q generation is the need for a base clock that operates twice as fast as the generated I/Q references. In applications where such a base clock is not readily available, other approaches have been taken for I/Q generation. For example, polyphase filters and various timing delay measures have been used to construct I and Q signal references. Not only are these approaches inherently cumbersome, requiring numerous extraneous components and measures, they typically generate just one output, either the I reference or Q reference, but not both concurrently. These approaches necessitate power- and area-intensive filters, delay lines, control loops, and the like.
There is therefore a need for a system and method by which I and Q references may be more simply and conveniently generated. There is a need for such system and method, in certain applications, by which discrete and adjustable clock phasing is generated for interpolating signals between the resulting I and Q references. There is also a need for such system and method whereby selectively phased interpolated signals may be conveniently generated with respect to the I and Q signal references.